The present invention broadly relates to a new and improved construction of a pipe coupling for coupling together the pipe ends of pipes or conduits or the like which are to be interconnected.
Generally speaking, the present invention relates to a new and improved construction of a pipe coupling for coupling together the pipe ends of pipes or conduits or the like which are to be interconnected and possessing a clampable housing having approximately the shape of a tightening clamp or collar and capable of being clamped about the pipe ends. The housing is provided at its end faces with annular inwardly flexed or deformed flanges as well as a sealing gasket enclosed in the housing and which possesses a substantially C-shaped axial or longitudinal cross-sectional configuration. This sealing gasket is open towards the inside and possesses clamping rings structured as sealing lips and is supported in axial direction in the housing. These clamping rings are provided on their inner surfaces with radially distributed claws or claw-like elements which, by tightening the housing, are caused to dig into the outer jacket surfaces of the pipe ends which are to be interconnected.
An example of a prior art pipe coupling of this type is disclosed, for instance, in the Swiss Pat. No. 620,509, which is cognate to the German Patent Publication No. 2,731,465 and the U.S. Pat. No. 4,119,333, granted Aug. 10, 1978.
The abovementioned known pipe coupling possesses clamping rings having the form of substantially hollow truncated cones. These clamping rings rest in the axial direction with their outer diameter in the fillet or throat between the flanges of the end faces and the inner wall of the housing. The clamping rings of this known pipe coupling are laminated on their inner surfaces with radial incisions forming lamellae or tabs, wherein the lamellae overlap one another in an imbricated fashion. The free end edges of each of these lamellae thus form claws on the inner diameter of the clamping ring which are intended to dig or grip into the outer jacket or shell surface of the pipe ends to be interconnected during tensioning or clamping of the housing and to be fixedly anchored thereat.
The depth of penetration of these free end edges of the lamellae of the known pipe coupling is dependent, on the one hand, on the extent to which the housing is tightened and, on the other hand, is especially dependent on the material of the pipes.
It will be appreciated that with pipes made from soft, relatively easily plastically deformable materials, the clamping rings of the known pipe coupling leave marks on the outer surface of the pipes which are excessively deep and moreover leave even deeper marks or scoring with the passage of time. These marks weaken to a substantial degree the tensile strength of the pipes. This is especially true for non-reinforced pipes and for reinforced pipes made from a synthetic material or plastic and also for pipes made from certain lightweight metallic alloys.
It is further observed that the tensile strength of a pipe connection made with the abovementioned known pipe coupling is very limited with pipes made of such materials. Should such a connection or joint between pipes made from comparatively soft or pliable material be subjected to a high tensile stress, for example, because the lengths of the pipes have contracted as a result of cooling or as a result of internal compressive stresses, then the substantially soft pipe material cannot resist the penetration of the free end edges of the lamellae of the clamping rings. These lamellae of the clamping rings no longer then serve as clamping elements, but more like planing tools that cut or shave off the outer surfaces of the ends of the pipes which are pulled from the pipe coupling as a result of the tensile stresses acting on the pipe joint or connection. The clamping effect of the pipe coupling is then lost when the lengths of the pipes later expand and return to their original dimension.
There is a pragmatic rule which applies for synthetic or plastic pipes and which states that gripping or clamping elements or claws should penetrate to a maximum of approximately ten percent of the thickness into the outer surface of the pipe in order to not significantly weaken the tensile strength of the pipes. The depth of penetration of the free end edges of the lamellae of the previously mentioned known pipe coupling is, however, as already mentioned, not limited and therefore indeterminate.